The conversion of light to electrical energy is a critical step in the organic photovoltaic charge generation mechanism. This energy transfer first requires the absorption of light by the photoactive layer materials. The standard source of light for photovoltaics is the sun. It is therefore required to match the polymer absorption with the solar spectrum. In general, the more light absorbed (extinction coefficient) and greater spectral overlap of the absorbing polymer with the solar spectrum, the higher the short-circuit current density in devices.
A common method for increasing the spectral light absorption of semiconducting polymers is by decreasing the bandgap. This can be achieved by altering the polymer backbone by using alternating copolymers of an electron rich and deficient monomer units. Decreasing the polymer bandgap red-shifts the absorbance, allowing a greater portion of the solar spectrum to be absorbed. Broadening the absorption range allows for additional photon absorption, which may provide an avenue for further improvements to device performance.
There exists a need to enhance light absorption in organic photovoltaics devices to improve power conversion efficiency.